[7alpha-18F]fluoro-17alpha-methyl-5alpha-dihydrotestosterone: a ligand for androgen receptor-mediated imaging of prostate cancer.

We have synthesized a 18F-labeled androgen, [7alpha-18F]fluoro-17alpha-methyl-5alpha-dihydrotestosterone, in a no-carrier-added radiosynthesis by exchange of 18F- (tetrabutylammonium fluoride) with the 7beta-tosyloxy of 17alpha-methyl-5alpha-dihydrotestosterone. The nonradioactive steroid binds with high affinity and specificity to the androgen receptor and binds poorly, if at all, to other steroid receptors and plasma sex hormone binding globulin. The 7alpha-18F-androgen concentrates markedly in the prostate of rats by an androgen receptor-dependent mechanism. It is likely that [7alpha-18F]fluoro-17alpha-methyl-5alpha-dihydrotestosterone will be an excellent positron emission tomography imaging agent for prostate cancer.